Tractor-mounted mower

ABSTRACT

A three-point hitch-mounted mower has a main frame that is mounted on and vertically adjustable with the tractor hitch. A generally fore-and-aft subframe is swingably mounted on the main frame on a transverse pivot, and the forward end of the subframe is connected to the tractor drawbar so that the rearward end of the subframe raises at a more rapid rate than the main frame. A transversely extending drag bar is universally pivoted to the main frame and carries a yoke at its outer end, a mower driving head being pivotally connected to the yoke for swinging about a fore-and-aft axis. A transversely extending cutter bar extends outwardly from the driving head and is driven thereby, and the driving head is connected to the rearward end of the subframe by a chain which causes the driving head to rock and thereby raise the cutter bar as the subframe raises, the chain having a predetermined amount of slack when the cutter bar is in operating position to allow the outer end of the cutter bar to float downwardly. A tension spring also extends between the rearward end of the subframe and the driving head offset from the driving head pivot, so that the spring partly counterbalances the weight supported on the mower shoes at the inner and outer ends of the cutter bar, a chain being mounted in parallel with the spring to limit the spring extension and raise the inner end of the cutter bar after the main frame and subframe raise a predetermined amount.

United States Patent [191 Nelsen et al.

[ TRACTOR-MOUNTED MOWER [75] Inventors: Arlyn Ray Nelsen; Wilfred LeeRoySteuerwald, both of Ottumwa, Iowa [73] Assignee: Deere & Company,Moline, [1].

[22] Filed: July 6, 1972 [21] Appl. No.: 269,344

[52] US. Cl 56/15.2, 56/10.4, 56/16.2, 56/282 [51] Int. Cl A0ld 55/28[58] Field of Search. 56/254, 10.2, 10.4, 10.9, 14.9, 56/15.1, 15.2,16.2, 271, 276-288 [56] References Cited UNITED STATES PATENTS 2,917,88912/1959 Vatz 56/10.4 2,580,266 12/1951 Abgarian. 56/10.4 2,637,9665/1953 Richey 56/10.4 2,673,437 3/1954 Pollock et a]... 56/1 1.9

2,779,145 l/l957 Smith 56/10.4

2,932,931 4/1960 Elfes 56/l0.4 3,014,328 12/1961 Scarnato et a] 56/15.33,151,430 10/1964 Wathen et al. 56/15.2 3,234,718 2/1966 Wathen 56/l0.9

Primary Examiner-Russell R. Kinsey [5 7 ABSTRACT A three-pointhitch-mounted mower has a main frame [451 Feb. 12, 1974 that is mountedon and vertically adjustable with the tractor hitch. A generallyfore-and-aft subframe is swingably mounted on the main frame on atransverse pivot, and the forward end of the subframe is connected tothe tractor drawbar so that the rearward end of the subframe raises at amore rapid rate than the main frame. A transversely extending drag baris universally pivoted to the main frame and carries a yoke at its outerend, a mower driving head being pivotally connected to the yoke forswinging about a fore-andaft axis. A transversely extending cutter barextends outwardly from the driving head and is driven thereby, and thedriving head is connected to the rearward end of the subframe by a chainwhich causes the driving head to rock and thereby raise the cutter baras the subframe raises, the chain having a predetermined amount of slackwhen the cutter bar is in operating position to allow the outer end ofthe cutter bar to float downwardly. A tension spring also extendsbetween the rearward end of the subframe and the driving head offsetfrom the driving head pivot, so that the spring partly counterbalancesthe weight supported on the mower shoes at the inner. and outer ends ofthe cutter bar, a chain being mounted in parallel with the spring tolimit the spring extension and raise the inner end of the cutter barafter the main frame and subframe raise a predetermined amount.

28 Claims, 9.Drawing Figures PATENTED 3.791 1 l5 SHEET t (If 6 M FIG.9

PATENTED FEB] 2I974 SHEET 5 OF 6 PAYENIEB FEB I 2 i974 SHEET 6 BF 6TRACTOR-MOUNTED MOWER BACKGROUND OF THE INVENTION This invention relatesto a reciprocating cutter bar type mower and more particularly to amechanism for mounting the mower on a tractor.

It is well known to mount a mower on the three-point hitch system of atractor by means of a mechanism which supports the mower cutter barlaterally of the tractor with the inner end of the cutter bar outsidethe tractor wheels. It is also known to provide a mounting system whichraises and lowers the cutter bar with the vertical adjustment of thethree-point hitch system.

While earlier mowers of said type generally used a Pitman drive poweredfrom the tractor power take-off shaft, many of the mounted mowers haveutilized a wobble-type driving head mounted at the inner end of thecutter bar, the driving head being conventionally driven by a powershaft from the power take-off and a belt drive having a driven sheaveconnected to the driving head. In such mowers, it is known to mount thedriving head on a generally fore-and-aft pivot so that the cutter barand driving head are swingable about the pivot adjacent the inner end ofthe cutter bar, the pivot being provided in a yoke mounted on the outerend of a drag bar, the inner end of which is pivotally connected to amain frame carried by the three-point hitch. It is further known toprovide a mechanism for initially swinging the driving head to raise theouter end of the cutter bar as the main mower frame is raised andthereafter to raise both the inner and outer ends of the cutter bar asthe main frame is raised.

In such mowers, it has also been conventional to provide spring meansfor counterbalancing the weight supported on the inner and outer shoeson the cutter bar. Also, the cutter bars are conventionally manuallyswingable upwardly and over center from their raised position to afolded or transport position, it being also known to provide a lockingdevice for locking the cutter bar in the transport position. It is alsoknown to permit the drag bar to swing about a vertical pivot so that thecutter bar swings rearwardly to a folded back position when it strikesan obstruction to prevent damage to the cutter bar, a tow bar beingconventionally provided between the drag bar and the tractor frame,which separates to permit the drag bar to swing rearward when apredetermined amount of tensile stress beyond the normal tensile stressin the tow bar is experienced.

SUMMARY OF THE INVENTION According to the present invention, there isprovided an improved mower design, that is of simple and ruggedconstruction, having improved operation and dependability. Morespecifically, there is provided an improved mechanism for mounting amower on a tractor. Still more specifically, there isprovided animproved mechanism for mounting a mower on a three-point hitch system ofthe tractor and for controlling the position of the mower through thethree-point hitch system.

An important feature of the invention resides in the fact that the moweris easily attachable to tractors having Category I or Category IIthree-point hitches without utilizing special tools. Also, the mowerframe has provisions for easily converting the mower from wide tread tonarrow thread positions without additional parts. More specifically, themower is converted from one position to the other by shifting themounting loca tion of the drag bar on the main mower frame and reversingparts in the lift mechanism.

Another feature of the invention resides in the provision of a subframewhich rocks relative to the main mower frame as the main frame raises toexaggerate the movement ofthe three-point hitch, the exaggeratedmovement of the subframe being transmitted to the driving head for thecutter bar to raise the cutter bar as the three-point hitch raises.Also, sufficient slack is provided in the connection between thesubframe and the driving head to allow the outer end of the cutter barto float downwardly for cutting on down slopes, the cutter bar raisingonly after a predetermined amount of vertical adjustment of the hitchwith the outer end of the cutter bar raising first.

Another feature of the invention resides in the provision of a linkagebetween the main frame and the tractor drawbar to limit the downwardmovement of the main frame, thereby establishing the lowered operatingposition of the main frame.

Still another feature of the invention resides in the provision of asingle spring which counterbalances part of the weight of both the innerand outer ends of the cutter bar. More specifically, the counterbalancespring is attached to the driving head for the cutter bar offset fromthe pivot about which the cutter bar and driving head rotate, so thatthe spring creates a moment opposite from the moment created by theweight on the outer cutter bar shoe, while the vertical component of thespring force counterbalances the weight on the inner shoe. Also,alternate connecting points for the spring are provided on the drivinghead to vary the lever arm through which the spring acts, so that themechanism can be adjusted for different cutter bars.

Another feature of the invention resides in an improved device forlocking the cutter bar in a folded over or transport position, saidlocking being accomplished by locking a link in the lift mechanism tothe supporting structure for the driving head, thereby locking thedriving head to the support structure.

Another feature of the invention resides in the provision of improvedmeans for'adjusting the cutter bar tilt, said tilted adjustment beingaccomplished by adjusting the annular position of the yoke, whichpivotally supports the driving head, on the outer end of the drag bar.

Still another feature of the invention resides in the provision of animproved breakaway system in the mounting mechanism, whereby the cutterbar will break rearwardly about avertical pivot between the main mowerframe and the transversely extending structure which supports thedriving head and cutter bar. Also, the driving head is driven by a beltdrive, which is so located relative to the breakaway pivot that the beltdrive automatically disengages whenthe cutter bar breaks away. Also, thecutter bar is maintained in its laterally extending operating positionby a pull bar, which is under tension when the mower is operating and isprovided with a release mechanism which perrnits the pull bar toseparate when the tensional stress exceeds a predetermined value,allowing the mower to break away. Another feature of the inventionresides in the fact that the pull bar is connectible to the-yoke in thedriving head supporting structure at alternate locations for wide andnarrow positions of the cutter bar, so that a single pull bar can beutilized in either position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a left rear perspective ofthe mower and the rear end of the tractor on which it is mounted withthe mower in operating position.

FIG. 2 is a very similar to FIG. 1 but with the mower in the raisedposition.

FIG. 3 is a top rear perspective view of the mower in operating positionwith the right end of the mower cutter bar omitted and showing the mowerpositioned for use with a wide tread tractor.

FIG. 4 is a rear perspective view of the mower in transport positionwith the mounting mechanism positioned for a narrow tread tractor.

FIG. 5 is a schematic rear elevation view of the mower in operatingposition.

FIG. 6 is a view similar to FIG. 5 but with the mower in a raisedposition.

FIG. 7 is a schematic view similar to FIG. 5 but with the outer end ofthe cutter bar angled downwardly to a maximum down float position of themower.

FIG. 8 is an enlarged right side and top perspective view of the mowerdriving head and a portion of the mounting mechanism.

FIG. 9 is a schematic rear view illustrating the forces exerted by thecounterbalance spring and the weight of the mower.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is embodied in amower which is attachable to a tractor 10, only the rearward portion ofwhich is shown in the drawings. The tractor is of conventionalconstruction and includes a pair of rear axle housings 12 from whichrear axles 13 project, a pair of rear drive wheels 14 being mounted onthe opposite axles 13. As is well known, the wheels 14 are adjustable onthe axles 13 to vary the tread width of the tractor.

As is also conventional, the tractor includes a rearward three-pointhitch 16 including a pair of rearwardly extending, vertically swingablelower links 17, the vertical positions of which are controlled by a pairof lift arms 18, and a vertically swingable central upper link 19. Aconventional laterally swingable drawbar 20 extends rearwardly from thetractor between the lower links, and a PTO output shaft 22 also extendsrearwardly from the tractor immediately above the draw bar, the PTOshaft being on the centerline of the tractor centrally between the lowerlinks 17.

The mower has a main frame, indicated generally by the numeral 24,mounted on the tractor three-point hitch 16 for vertical adjustmenttherewith. The main frame includes an inverted U-shaped member 26 havinggenerally upright right and left legs 27 and 28 respectively connectedby an upper transverse portion 29, the upper part of the legs 27 and 28being inclined somewhat upwardly and forwardly. A transverse beam 30interconnects the lower ends of the legs 27 and 28. A pair of generallyupright fore-and-aft C-shaped members 31 and 32 respectively have theirends connected to and extend forwardly from the right and left legs 27and 28, and a second transverse beam 33 forwardly of the beam 30interconnects the lower parts of the C- shaped members 31 and 32. As isapparent, the upper link 19 is pivotally connected to the transverseportion 29 of the main frame, while the opposite lower links 17 arerespectively pivotally connected to the opposite C- shaped members 31and 32 by means of transverse pivots, so that the main frame 24 raisesand lowers with the three-point hitch. Bushings are provided on thetransverse pivots if the mower is mounted on a Category II three-pointhitch rather than a Category I hitch, and alternate attaching holes arepivoted for the top link 19 for the alternate hitches.

A pair of aligned transverse pivots 34 and 35 are respectively mountedon the legs 27 and 28 of the main frame and extend inwardly therefrom,and a subframe 36 is swingably mounted on the pivots 34 and 35. Thesubframe is disposed in a generally horizontal, foreand-aft positionwhen the main frame is in its lower operating position and includes agenerally fore-and-aft arm 38 swingably mounted intermediate its ends onone of the pivots, a shorter arm 39 havingits forward end mounted on theother pivot, and a transverse portion 40 bolted to the rearward ends ofthe arms 38 and 39. The shorter arm 39 is angled inwardly, and the armsare reversible, so that when the long arm 38 is mounted on the rightpivot 34, as illustrated in FIG. 3, the transverse portion 40 isconnected to the arms on the right side of the tractor centerline,while, when the longer arm 38 is mounted on the left'pivot 35, asillustrated in FIG. 4, the transverse portion 40 is connected to thearms on the left side of the tractor centerline.

A chain 42 has one end connected to the forward end of the longersubframe arm 38 and its opposite ends connected to one of two alternateears 43 extending forwardly from the main frame beam 33 on oppositesides of the centerline. The chain includes an attach ment link 44intermediate its opposite ends, which is connected to the tractordrawbar by a fastener 45. When the arm 38 is disposed on the right sideof the subframe, as shown in FIG. 3, the drawbar is swung to the rightand the chain is attached to the right-hand ear 43, while the drawbar isswung to the left and the chain is attached to the left-hand ear 43 whenthe subframe is reversed.

The lower section of the chain 42 between the drawbar and the main framefunctions as a stop, which limits the downward movement of the mowermain frame 24. As best seen in FIG. 8, the lower section of the chain isunder tension and extends downwardly and rearwardly from the drawbarwhen the main frame is in operating position. Since the main frame movesupwardly and rearwardly as the three-point hitch is raised, the distancebetween the drawbar and the attachment point on the frame is reduced asthe frame raises and the lower chain section becomes slack. The upperportion of the chain, which serves as a linkage between the drawbar andthe forward end of the arm 38, is under tension and causes the forwardend of the subframe to swing downwardly relative to the main frame asthe main frame raises. Consequently, the rear transverse portion 40 ofthe subframe swings upwardly relative to the main frame as the mainframe raises, multiplying or exaggerating the movement of the mainframe. A pair of stops 46 respectively extend inwardly from the oppositelegs 27 and 28 of the main frame and serve to limit the downwardmovement of the rearward portion of the subframe relative to the mainframe, a small amount of slack being provided in said upper portion ofthe chain when the mower is in operating position.

A fore-and-aft pivot 48 is removably attached to the transverse beam 30at alternate locations on the transverse beam, the forward end of theivot extending through alternate holes 49 in the beam. A yoke 50 isrotatably mounted on the pivot 48, and a pivoting member 52 is rockableabout a generally vertical pivot between the opposite arms of the yoke50. The foreand-aft axis of the pivot 48 and the vertical swinging axisof the pivoting member 52 provide a universal-type pivoting connectionbetween the main frame and a laterally extending support structure,indicated generally by the numeral 54. The support structure includes alaterally extending, tubular drag bar 56, having its inner end connectedto the pivoting member 52 by means of an adjusting mechanism 57, whichpermits axial adjustment of the drag bar 56 relative to the pivotingmember 52. In the illustrated embodiment, the adjusting mechanismincludes a socket in which the drag bar is keyed and is axiallyslidable, the drag bar being shifted by turning a cap screw attached tothe drag bar in a threaded block attached to the socket. The supportstructure also includes a generally horizontal bifurcated member or yoke58 having front and rear later- I ally extending arms 59 and 60respectively and a generally flat central portion 62, which is providedwith a transverse bore in which the end of the drag bar is rotatablyreceived. The drag bar extends through the bore in the central portion62 and a radial arm 64 is secured to the end of the drag bar adjacent tothe yoke 62. An adjusting screw 66 has its lower end rotatably receivedin a socket 67 on the central portion of the yoke and extends through athreaded pivot 68 carried by the upper end of the arm 64. As isapparent, the above provides an adjusting mechanism for adjusting theangular position of the yoke relative to the drag bar, rotation of theadjusting screw 66 changing the distance between the yoke and the end ofthe arm 64 to rock the yoke about the end of the drag bar.

A mower driving head, indicated generally by the numeral 70, isswingably supported between the opposite arms 59 and 60 of the yoke 58for rotation about a generally fore-and-aft axis. The driving head is ofthe type that converts rotary to reciprocating movement, such drivingheads being utilized on many commercially available mowers. The drivinghead has a housing 72 and a fore-and-aft input shaft 74 which isrotatably received in and extends rearwardly through the rear arm 60 ofthe yoke 58. A pivot 75 coaxial with the input shaft 74 extendsforwardly from the housing 72 and is rotatably received in the frontyoke arm 59, so that the driving head rocks about the input shaft 74 andthe pivot 75.

A cutter bar 76 of known .construction is attached to the underside ofthe housing 72 and extends laterally outwardly from the driving head,which has a generally forwardly extending reciprocating arm 78 attachedto the knife of the cutter bar 76. As is conventional, the cutter barhas an inner shoe 80 and an outer shoe 82, which are respectivelymounted on the cutter bar at the inner and outer ends thereof and ridealong the ground to support the weight of the mower not supported by thetractor.

The driving head 70 is driven by a drive system from the tractor PTOshaft 22, the drive system including a conventional drive shaft 84providedwith a pair of universal joints adjacent its front and rearends, the forward end being connectible to the PTO shaft and therearward ends being connected to a fore-and-aft drive shaft rotatablysupported on the upper arm of the yoke 50. A drive sheave 88 is mountedon the end of the rearward drive shaft 86 and drives a driven sheave 90mounted on the driving head input shaft 74 through a drive belt 91. Aflywheel 92 is provided on the input shaft rearwardly of the drivensheave, which is shielded by a shield 93, the drive sheave 88 beingsimilarly shielded by a shield 94. The tension in the belt 91 can beadjusted by axially shifting the drag bar 56 relative to the member 52by means of the adjusting mechanism 57, as previously described.

A pull bar 96 is attachable to alternate attaching brackets 97 and 98 onthe central portion 62 of the yoke 58, the forward end of the pull barbeing connected to the main frame 24 by means of a member 99 extendinglaterally from the forward end of the right side C-shaped frame member31. Since the support structure 54 is free to swing rearwardly about theaxis of the pivot member 52, the pull bar is under tension as thetractor and mower advances. A release mechanism 100, of well knownconstruction, is provided in the pull bar to allow the pull bar toseparate when the tension in the pull bar exceeds a predetermined amountas the result of the cutter bar striking an obstruction. As is wellknown, the release mechanism is adjustable to vary the force which ittakes to separate the pull bar, and the pull bar includes telescopingportions, which slide relative to one another when the release mechanism100 releases, the pull bar in the illustrated embodiment allowingapproximately 55 breakaway of the cutter bar from the operating positionillustrated. Since the supporting structure pivots about the axis of thepivot member 52 during a breakaway, and the drive sheave 88 does notchange positions during the breakaway and is located rearwardly of theaxis of the member 52, the distance between the drive and driven sheavesdecreases during a breakaway of the center bar to automaticallydisengage the drive when the cutter bar strikes an obstruction andbreaks away. The alternate attaching brackets 97 and 98 are provided sothat the same pull bar can be utilized when the mower is positioned ineither its wide or narrow position, the forward bracket 97 beingutilized when the mower is positioned for wide tread operation asillustrated in FIGS. 3 and 8.

A chain 102 has one end attached to the transverse or rearward portion40 of the subframe 36 by means of a fastener 104 and its opposite endattached to one end of an arcuate link 106. The other end of the arcuatelink 106 is pivotally connected to the driving head and is disposedbetween a pair of upright brackets 108 on top of the housing 72, thebrackets 108 being provided with alternate pivot holes to permit thepivotal connection of the lower end of the link, 106 at alternatelocations. A helical tension spring 112 has its opposite ends connectedto links in the chain 102 proximate to the opposite ends of the chain.The chain extends through the center of the spring, and the distancebetween the attaching points on the chain is greater than the staticlength of the spring, so that when the spring is unstretched, there isconsiderable slack in the chain. As is apparent, the chain limits theextension of the spring, which can be adjusted by shifting the spring toa different link in the chain.

A second chain 1l4 has one end attached to the transverse or rearwardportion 40 of the subframe 36 by means of a fastener 116, which isadjacent to the fastener 104. The chain H4 is trained around a pulley138 which is rotatably supported on the upper arm of the yoke 50 forrotation about a fore-and-aft axis generally below the attachment to thesubframe. The other end of the chain 114 is attached to a lever arm 120by means of an apertured link 122, the lower end of the arm 120 beingpivotally connected to the driving head housing 72 on a fore-and-aftpivot 124 extending rearwardly from the rear bracket 108. The housing'72 is provided with a generally upright fore-and-aft abutment 126adjacent to the inner side of the lower end of the lever arm 120, sothat the lever arm 120 is free to rock in a clockwise direction (whenviewed from the rear of the machine), but engages the abutment when itis rocked in a counterclockwise direction. As is apparent, rotation ofthe lever arm in the counterclockwise direction causes the driving headto rotate in the same direction about the fore-and-aft driving headpivot. The length of the chain 114 is such that there is a predeterminedamount of slack in the chain when the main frame is in its loweredoperating position and the cutter bar is in a generally horizontalposition, and a tension spring 127 has its opposite ends connected tothe chain on opposite sides of the pulley 118 to take up the slack inthe chain.

The central portion 62 of the yoke 58 has an upright post 128 whichprojects through the apertured link 122 when the cutter bar is rotatedto its transport position, as shown in FIG. 4, and a fore-and-aft lockpin 130 is insertable through the upper end of the post 128 above thelink 122 when the cutter bar is in the transport position to lock thelever arm 120 and its associated link 122 to the yoke 58, therebylocking the driving head and consequently the cutter bar in thetransport position.

In operation, the mower is initially set in either its wide or narrowposition depending on the width of the tread of the tractor on which themower is mounted. The cutter bar is shown in its wide position in allthe drawings except FIG. 4, wherein it is illustrated in its narrowposition, which, in the illustrated embodiment, is 9 inches inwardly ofthe wide position. Thus, the pivot 48 is located 4% inches to the rightof the tractor centerline in the wide position of the mower and 4%inches to the left of the centerline in the narrow position. Similarly,the transverse portion 40 of the subframe is attached to the rearwardends of the subframe arms 38 and 39 4% inches to the right of thecenterline in the wide position and 4 inches to the left of thecenterline in the narrow position. To convert from the wide to thenarrow position, it is merely necessary to shift the location at whichthe pivot 48 is clamped to the main frame beam 30, the pivot 48extending through the alternate holes 49 in its alternate positions. Thetransverse portion 40 is then removed from the arms 38 and 39, the armsare then reversed, and the transverse portion 40 is again bolted to therearward ends of the arms 38 and 39. The 4% inch offset of the pointbetween the two attaching bolts from the tractor centerline shifts thetransverse portion 9 inches laterally and consequently shifts the pointof attachment of the chain 102 and the chain 114 9 inches laterally. Thepull bar 96 is also shifted from the attaching bracket 97 to theattaching bracket 98 on the yoke 58 when the mower is adjusted from thewide to the narrow positlOn.

When the mower is in operating position, as shown in H6. 5, there isslack in both the chain 114 and the chain 102., although the spring H2is partially stretched. The spring 112 exerts a counterbalancing forcewhich is applied to both the inner shoe and the outer shoe 82. As shownin PEG. 9, the weight supported on the outer shoe exerts a moment aboutthe pivot of the driving head equal to the weight of the outer shoetimes the distance D from the driving head pivot, which moment iscounteracted by the moment created by the force exerted by the springtimes the dis tance L that the spring is offset from the driving headpivot. The weight on the inner shoe 80 is counterbalanced by thevertical component of the force exerted by the spring 112. The amount ofcounterbalancing force for the outer shoe can be varied by changing thelength of the lever arm through which the spring force acts by utilizingthe alternate mounting holes for the link 106. For example, if ashorter, lighter weight cutter bar is utilized, the bottom mounting holeis utilized, while if a longer heavier cutter bar is utilized, the topmounting hole is used to provide a maximum lever arm L. The length ofthe lever arm and the spring 112 are initially chosen so that the springwill simultaneously counterbalance a substantial portion of the weightin boththe inner and outer shoes. Preferably, the inner shoe weight issomewhat greater than the weight on the outer shoe, the inner shoeweight preferably being approximately 80 lbs., while the weight on theouter shoes is approximately 35 lbs. Such weights will allow the cutterbar to closely follow the contour of the ground, while permitting it tofloat upwardly when it strikes a mound or other obstruction. Of course,the extension of the spring 1 12, when the cutter bar is in itsoperating position, depends on the particular links in the chain 102 towhich the opposite ends of the spring are attached, and the links areselected to provide a vertical component of the spring force thatcounterbalances all but approximately 80 lbs. of the weight on the innershoe. After the inner shoe weight is established, the outer shoe weightcan be adjusted by mounting the link in the alternate pivot holes aspreviously described.

when the mower is in its normal operating position, as shown in FIG. 5,the length of the chain 114 is selected so that there is substantialslack in the chain. The slack permits the driving head and the cutterbar attached thereto to swing downwardly to follow the contour of theground. The outer shoe 82 will float downwardly until the chain 114becomes taut, as shown in FIG. 7, wherein the mower is shown in itsmaximum down float position. Preferably, sufficient slack is provided inthe chain 11.4 to allow approximately 30 down float. The link 106 isarcuate so that it will clear the housing 72 as the cutter bar floatsdownwardly.

To raise the mower, the three-point hitch is raised, raising the mainrame 24. Since the forward end of the subframe 36 is held by the chain42, the subframe swings relative to the main frame with the rearward endof the subframe raising at a more rapid rate than the main frame. Therelative movement between the subframe and the main frame pulls on thechain 114, the initial portion of the movement taking up the slack inthe chain 114, and after the chain is taut, the chain pulls on the lever120, which engages the abutment 126 to swing the driving head 70 and thecutter bar 76 upwardly about the driving head pivot. Since the drag bar56 is pivotally connected to the main frame, the inner shoe remains onthe ground. However, as the rearward end of the subframe 36 raises, thefloat spring 112 elongates, reducing the weight on both the inner andthe outer shoe. When the lift chain 1 14 tightens to start the raisingof the outer shoe 82, additional weight is transferred to the inner shoe80, and the float spring 112 continues to elongate until the slack inthe chain 102 is removed. At this time, additional raising of therearward end of the subframe, raises the inner shoe while the outer'shoe is also being raised, the mower being shown in the raised positionin FIG. 6 and FIG. 2. After the mower is placed in the raised position,it can be manually folded over to the transport position shown in FIG.4.

To again place the mower in operation position, the main frame islowered until the chain connection between the drawbar 20 and the mainframe becomes taut, thereby establishing the lowermost or operatingposition of the mower.

To adjust the tilt of the cutter bar about a horizontal, transverseaxis, the adjusting screw 66 is rotated to rock the yoke 58 andconsequently the cutter bar about the transverse axis of the drag bar aspreviously described.

When the cutter bar breaks away, as previously described, raising thehitch causes the spring 112 to stretch and exert a forward pull on thedriving head, which swings the support structure forwardly to its normalposition, the release mechanism 100 automatically relatching when thesupport structure reaches its normal position, so that the operator canrestore the mower to its operating condition without leaving thetractor.

We claim:

1. A mower attachable to a tractor having a vertically adjustable hitchand comprising: a vertically adjustable main frame mounted on thetractor hitch; a transverse pivot means on the main mower frame; asubframe swingably mounted on said pivot means; a first linkage meansconnecting the subframe to the tractor forwardly of the pivot means tocause the subframe to swing relative to the main frame as the main frameraises; a transversely extending support structure having one endpivotally connected to the main frame and having a generallyfore-and-aft pivot means adjacent its outer end; a mower driving headpivotally mounted on said fore-and-aft pivot means; a cutter barconnected to and extending laterally outwardly from the driving head andoperatively driven thereby; a spring means operatively connected to oneof said frames and to the driving head for partly counterbalancing theweight of the driving head and cutter bar; and a second linkage meansoperatively connected to the driving head at a point offset from saidfore-and-aft pivot means and to the subframe rearwardly of thetransverse pivot means so that the driving head is rocked about saidfore-andaft pivot means at least during a portion of the rockingmovement of the subframe relative to the main frame to raise the outerend of the cutter bar.

2. The invention defined in claim 1 wherein the main frame includes agenerally U-shaped member having generally upright legs, the transversepivot means being mounted on the legs, and the subframe includes a pairof arms respectively pivotally connected to the legs and a rearwardportion interconnecting the arms rearwardly of the pivot means, thefirst linkage means being connected to one of said arms forwardly of thepivot means.

3. The invention defined in claim 2 wherein the second linkage means isconnected to the rearward portion offset from the fore-and-aftcenterline between the legs of the main frame member, the subframe armsbeing removably connected to the main frame member and reversible sothat the second linkage means is connected to the subframe in alternatepositions when the arms are reversed.

4. The invention defined inclaim 1 wherein the tractor has a rearwardlyextending drawbar, and the first linkage means includes a chainconnecting the sub frame to the drawbar.

5. The invention defined in claim 4 and including a second chainconnecting the main frame to the drawbar to limit the downward movementof the main frame and thereby establish the lowermost position of themain frame.

6. The invention defined in claim 1 wherein the support structureincludes a transversely extending drag bar having its inner endpivotally connected to the main frame, a yoke having means defining saidfore-and-aft pivot means, and tilt adjusting means connecting the yoketo the outer end of the drag bar for selective adjustment of the yokeabout a generally transverse axis to vary the attitude of thefore-and-aft pivot means about said axis and thereby adjust the tilt ofthe cutter bar.

7. The invention defined in claim 1 wherein the support structure ispivotally connected to the main frame at alternate transversely spacedlocations to vary the lateral position of the cutter bar relative to thetractor, and the subframe arms are reversible on said transverse pivotmeans so that the second linkage means and the spring means areselectively connected to the subframe at alternate locations toaccommodate the alternate positions of the support structure.

8. The invention defined in claim 1 wherein the tractor includes a PTOdrive shaft, and the driving head is driven by a drive system includinga drive sheave selectively journaled on the main frame at alternatelocations corresponding to the alternate location of the supportstructure and connected to the PTO shaft by a drive shaft, a drivensheave mounted on the driving head and serving as an input thereto, anda belt drivingly connecting the drive sheave to the driven sheave.

9. The invention defined in claim 1 wherein the spring means is atension spring operatively connected to the driving head at a pointoffset from the fore-andaft pivot means so that the force exertedthereby tends to rotate the driving head in the opposite direction fromthe weight of the cutter bar to partly counterbalance the weightsupported at the outer end of the cutter bar, the spring also exerting aforce tending to rotate the supporting structure upwardly about itspivot connection to the main frame to partly counterbalance the weightsupported on the inner end of the cutter bar.

it). The invention defined in claim 9 wherein the spring means isattachable to the driving head at alternate locations to selectivelyvary the offset from the pivot means and thereby vary the counterbalanceforce at the outer end of the cutter bar.

11. The invention defined in claim 1 wherein the second linkage meansincludes a flexible element having a predetermined amount of slack whenthe cutter bar is supported in a level position and the main frame is inits lowered position, the pivoting movement of the subframe as the mainframe raises initially taking up the slack and thereafter causing thedriving head to rock about the fore-and-aft pivot means to raise theouter end of the cutter bar.

12. The invention defined in claim 11 wherein the second linkage meanslimits the rocking movement of the driving head and thereby limits thedownward movement of the outer end of the cutter bar, the predeterminedslack in the linkage means allowing a predetermined amount of downwardmovement of the outer end of the cutter bar relative to the inner end.

13. The invention defined in claim 1 wherein the cutter bar is swingableupwardly from a horizontal operating position past a vertical positionto an inclined folded position and including a locking means mounted onthe support structure and operatively connectible to the second linkagemeans to lock the driving head to the support structure with the cutterbar in its folded position.

14. A mower attachable to a tractor having a vertically adjustable hitchand comprising: a vertically adjustable main frame mounted on thetractor hitch and including a generally U-shaped member having generally upright legs; a pair of coaxial transverse pivot means respectivelymounted on the opposite legs; a subframe including a pair of armsrespectively mounted on the pivot means and a rearward portioninterconnecting the arms rearwardly of the pivot means; a first linkagemeans connecting at least one of said arms forwardly of the pivot meansto the tractor, to cause the rearward portion of the subframe to swingupwardly about said pivot means as the main frame raises; a transverselyextending support structure having one end pivotally connected to themain frame and carrying a generally fore-and-aft pivot means adjacentits outer end; a mower driving head swingably mounted on saidfore-and-aft pivot means; and a cutter bar connected to and extendinglaterally from the driving head and swingable therewith from a generallyhorizontal operating position to an upwardly and outwardly inclinedraised position; and a second linkage means operatively connecting thedriving head to the subframe rearwardly of the transverse pivot means sothat the driving head rocks about said fore-and-aft pivot means duringat least a portion of the upwardly swinging movement of the rearwardportion of the subframe to raise the cutter bar from its horizontalposition to its raised position.

15. The invention defined in claim 14 wherein the second linkage meansis connected to the rearward portion of the subframe offset from thefore-and-aft centerline of the tractor and the subframe arms are reversible so that the point of connection between the subframe and thesecond linkage means is located in alternate positions when the arms arereversed.

16. The invention defined in claim 14 wherein the tractor includes arearwardly extending drawbar and the first linkage means includes achain interconnecting one of said arms to the drawbar.

17. The invention defined in claim 16 and including a chain operativebetween the drawbar and the main frame to limit the downward movement ofthe main frame.

18. A mower attachable to a tractor having a vertically adjustable hitchand a rearwardly extending drawbar, said mower comprising: a verticallyadjustable main frame mounted on the tractor hitch; a pivot means on themain frame; a subframe swingably mounted on said pivot means; a firstlinkage means connecting the subframe to the tractor to cause thesubframe to pivot relative to the main frame as the main frame raises; aflexible linkage between the drawbar and the main frame for limiting thedownward movement of the main frame to establish the lowermost operatingposition of the mower; a transversely extending support structure havingone end pivotally connected to the main frame and having a generallyforeand-aft pivot means adjacent to its outer end; a mower driving headpivotally mounted on said fore-and-aft pivot means; a cutter barconnected to and extending laterally outwardly from the driving head andoperatively driven thereby; and a second linkage means operativelyconnecting the driving head to the subframe so that the driving headrocks about said fore-and-aft pivot means at least during a portion ofthe rocking movement of the subframe relative to the main frame to raisethe outer end of the cutter bar during at least a portion of the raisingof the main frame.

19. The invention defined in claim 18 wherein said first linkage meansand said flexible linkage means comprise a chain having one endconnected to the main frame, the other end connected to the subframe,and connected to the drawbar intermediate its opposite ends.

20. A mower comprising: a frame means; a transversely extending supportstructure having one end pivotally connected to the frame means andhaving a generally foreand-aft pivot means adjacent to its outer end; amower driving head pivotally mounted on said fore-and-aft pivot means; acutter bar connected to and extending laterally outwardly from thedriving head and operatively driven thereby and swingable with thedriving head about said fore-and-aft pivot means from a generallyhorizontal operating position, to an up wardly and outwardly inclinedraised position, and thereafter to an upwardly and inwardly inclinedfolded transport position; a linkage means operatively connecting thedriving head to the frame means for rocking the driving head and thecutter bar from said operating position to said raised position as theframe means raises; and locking means operative to lock the linkagemeans to the support structure when the driving head and cutter bararerotated to said transport position.

21. The invention defined in claim 20 wherein the linkage means includesan apertured element, and the locking means includes a generally uprightmember, extending upwardly from the supporting structure and extendiblethrough the apertured element when the cutter bar is shifted to itstransport position, and pin means extendible through the upright memberabove the apertured element to lock the apertured element on the uprightmember. I

22. A mower attachable to a tractor having a vertically adjustable hitchand a rearwardly extending power take-off shaft, said mower comprising:a vertically adjustable main frame mounted on the tractor hitch andincluding a generally U-shaped member having generally upright legs; apair of transversely aligned pivots mounted on the opposite legs; asubframe swingably mounted on said pivots and including a pair of armsrespectively mounted on the respective pivots and a rearward portioninterconnecting the arms rearwardly of the pivot means; a first linkagemeans connecting one of said arms to the tractor forwardly of the pivotmeans to cause the rearward portion of the subframe to raise relative tothe main frame as the main frame raises; a transversely extendingsupport structure having one end pivotally connectible to the main frameat alternate locations on opposite sides of the tractor centerline andhaving a generally fore-and-aft pivot means adjacent its outer end; amower driving head pivotally mounted on said fore-and-aft pivot means; acutter bar connected to and extending laterally outwardly from thedriving head and operatively driven thereby; a drive system connectingthe power take-off shaft to the driving head and including a drivesheave rotatably supported on the main frame for lateral adjustmentbetween alternate positions on opposite sides of the centerline andconnected to the power take-off shaft by a drive shaft, a driven sheavedrivingly connected to the driving head coaxial with the fore-and-aftpivot means, and a belt drive interconnecting the drive and drivensheaves; and a second linkage means operatively connecting the drivinghead to the rearward portion of the subframe, at least a portion of thesubframe being reversible so that the second linkage means is connectedto the subframe at alternate locations corresponding to the alternatelocations of the support structure.

23. The invention defined in claim 22 and including a spring meansconnected to the driving head and the rearward portion of the subframesubstantially the same location as the second linkage means.

24. A mower comprising: a vertically adjustable main frame, a subframeswingably mounted on the main frame and operatively connected to themain frame for vertical adjustment therewith and rocking movementrelative thereto as the main frame raises; a transversely extendingsupport structure having one end pivotally connected to the main frameand having a generally fore-and-aft pivot means adjacent its outer end;a mower driving head pivotally mounted on said foreand-aft pivot means;a cutter bar connected to and extending laterally outwardly from thedriving head and operatively driven thereby; a tension spring meansoperatively connected to a portion of the subframe that raises at a morerapid rate than the main frame during the raising of the main frame;means connecting the spring means to the driving head at a point offsetfrom the fore-and-aft pivot means so that the force exerted by thespring means tends to rotate the driving head in the opposite directionfrom the weight of the cutter bar to partly counterbalance the weightsupported at the outer end of the cutter bar, the spring means alsoexerting a force tending to rotate the supporting structure upwardlyabout its pivot connection to the main frame to partly counterbalancethe weight supported on the inner end of the cutter bar; and linkagemeans operatively connecting the driving head to the subframe so thatthe driving head is rocked about said fore-and-aft pivot means to raisethe outer end of the cutter bar at least during a portion of the rockingmovement of the subframe relative to the main frame.

25. The invention defined in claim 24 wherein the means connecting thespring to the driving head includes a chain connected in parallel withthe spring means to limit the extension of the spring means to apredetermined amount, the chain transmitting the vertical movement ofthe subframe directly to the driving head after said predeterminedamount of spring extension to raise the driving head about the pivotconnection between the support structure and main frame.

26. A mower attachable to a tractor having a vertically adjustable hitchand comprising: a vertically adjustable main frame mounted on thetractor hitch; a subframe swingably mounted on the main frame; a firstlinkage means connecting the subframe to the tractor to cause thesubframe to pivot relative to the main frame as the main frame raises sothat a portion of the subframe raises at a faster rate than the mainframe; a transversely extending support structure having one endpivotally connected to the main frame and having a generallyfore-and-aft pivot means adjacent its outer ends; a mower driving headpivotally mounted on said fore-and-aft pivot means; a cutter barconnected to and extending laterally outwardly from the driving head andoperatively driven thereby; a spring means operatively connected to oneof said frames and to the driving head for partly counterbalancing theweight of the driving head and the cutter bar; and a flexible elementoperatively connected to the driving head at a point offset from thefore-and-aft pivot means and to said portion of the subframe to causethe cutter bar to raise about said fore-and-aft pivot means during thelatter portion of the raising motion of the main frame, the flexibleelement being provided with a predetermined amount of slack when thecutter bar is in a generally horizontal operating position, which slackis taken up during the initial raising movement of the main frame andpermits a predetermined amount of downward movement of the outer end ofthe cutter bar so that the cutter bar follows the contour of the ground.

27. The invention defined in claim 26 wherein the flexible element isconnected to the driving head through a lever swingably connected to thedriving head about a generally fore-and-aft axis and engageable with anabutment on the driving head to transmit the lifting force exerted bythe flexible element.

28. The invention defined in claim 27 and including a pulley mounted onthe subframe, the flexible element being trained around said pulley sothat the vertical movement of the subframe portion results in agenerally horizontal force, which is exerted on the driving head throughthe flexible element, the lever, and the driving head abutment.

1. A mower attachable to a tractor having a vertically adjustable hitchand comprising: a vertically adjustable main frame mounted on thetractor hitch; a transverse pivot means on the main mower frame; asubframe swingably mounted on said pivot means; a first linkage meansconnecting the subframe to the tractor forwardly of the pivot means tocause the subframe to swing relative to the main frame as the main frameraises; a transversely extending support structure having one endpivotally connEcted to the main frame and having a generallyfore-and-aft pivot means adjacent its outer end; a mower driving headpivotally mounted on said fore-and-aft pivot means; a cutter barconnected to and extending laterally outwardly from the driving head andoperatively driven thereby; a spring means operatively connected to oneof said frames and to the driving head for partly counterbalancing theweight of the driving head and cutter bar; and a second linkage meansoperatively connected to the driving head at a point offset from saidfore-and-aft pivot means and to the subframe rearwardly of thetransverse pivot means so that the driving head is rocked about saidfore-and-aft pivot means at least during a portion of the rockingmovement of the subframe relative to the main frame to raise the outerend of the cutter bar.
 2. The invention defined in claim 1 wherein themain frame includes a generally U-shaped member having generally uprightlegs, the transverse pivot means being mounted on the legs, and thesubframe includes a pair of arms respectively pivotally connected to thelegs and a rearward portion interconnecting the arms rearwardly of thepivot means, the first linkage means being connected to one of said armsforwardly of the pivot means.
 3. The invention defined in claim 2wherein the second linkage means is connected to the rearward portionoffset from the fore-and-aft centerline between the legs of the mainframe member, the subframe arms being removably connected to the mainframe member and reversible so that the second linkage means isconnected to the subframe in alternate positions when the arms arereversed.
 4. The invention defined in claim 1 wherein the tractor has arearwardly extending drawbar, and the first linkage means includes achain connecting the subframe to the drawbar.
 5. The invention definedin claim 4 and including a second chain connecting the main frame to thedrawbar to limit the downward movement of the main frame and therebyestablish the lowermost position of the main frame.
 6. The inventiondefined in claim 1 wherein the support structure includes a transverselyextending drag bar having its inner end pivotally connected to the mainframe, a yoke having means defining said fore-and-aft pivot means, andtilt adjusting means connecting the yoke to the outer end of the dragbar for selective adjustment of the yoke about a generally transverseaxis to vary the attitude of the fore-and-aft pivot means about saidaxis and thereby adjust the tilt of the cutter bar.
 7. The inventiondefined in claim 1 wherein the support structure is pivotally connectedto the main frame at alternate transversely spaced locations to vary thelateral position of the cutter bar relative to the tractor, and thesubframe arms are reversible on said transverse pivot means so that thesecond linkage means and the spring means are selectively connected tothe subframe at alternate locations to accommodate the alternatepositions of the support structure.
 8. The invention defined in claim 1wherein the tractor includes a PTO drive shaft, and the driving head isdriven by a drive system including a drive sheave selectively journaledon the main frame at alternate locations corresponding to the alternatelocation of the support structure and connected to the PTO shaft by adrive shaft, a driven sheave mounted on the driving head and serving asan input thereto, and a belt drivingly connecting the drive sheave tothe driven sheave.
 9. The invention defined in claim 1 wherein thespring means is a tension spring operatively connected to the drivinghead at a point offset from the fore-and-aft pivot means so that theforce exerted thereby tends to rotate the driving head in the oppositedirection from the weight of the cutter bar to partly counterbalance theweight supported at the outer end of the cutter bar, the spring alsoexerting a force tending to rotate the supporting structure upwardlyabout its pivot connection to the main frame to partly couNterbalancethe weight supported on the inner end of the cutter bar.
 10. Theinvention defined in claim 9 wherein the spring means is attachable tothe driving head at alternate locations to selectively vary the offsetfrom the pivot means and thereby vary the counterbalance force at theouter end of the cutter bar.
 11. The invention defined in claim 1wherein the second linkage means includes a flexible element having apredetermined amount of slack when the cutter bar is supported in alevel position and the main frame is in its lowered position, thepivoting movement of the subframe as the main frame raises initiallytaking up the slack and thereafter causing the driving head to rockabout the fore-and-aft pivot means to raise the outer end of the cutterbar.
 12. The invention defined in claim 11 wherein the second linkagemeans limits the rocking movement of the driving head and thereby limitsthe downward movement of the outer end of the cutter bar, thepredetermined slack in the linkage means allowing a predetermined amountof downward movement of the outer end of the cutter bar relative to theinner end.
 13. The invention defined in claim 1 wherein the cutter baris swingable upwardly from a horizontal operating position past avertical position to an inclined folded position and including a lockingmeans mounted on the support structure and operatively connectible tothe second linkage means to lock the driving head to the supportstructure with the cutter bar in its folded position.
 14. A mowerattachable to a tractor having a vertically adjustable hitch andcomprising: a vertically adjustable main frame mounted on the tractorhitch and including a generally U-shaped member having generally uprightlegs; a pair of coaxial transverse pivot means respectively mounted onthe opposite legs; a subframe including a pair of arms respectivelymounted on the pivot means and a rearward portion interconnecting thearms rearwardly of the pivot means; a first linkage means connecting atleast one of said arms forwardly of the pivot means to the tractor, tocause the rearward portion of the subframe to swing upwardly about saidpivot means as the main frame raises; a transversely extending supportstructure having one end pivotally connected to the main frame andcarrying a generally fore-and-aft pivot means adjacent its outer end; amower driving head swingably mounted on said fore-and-aft pivot means;and a cutter bar connected to and extending laterally from the drivinghead and swingable therewith from a generally horizontal operatingposition to an upwardly and outwardly inclined raised position; and asecond linkage means operatively connecting the driving head to thesubframe rearwardly of the transverse pivot means so that the drivinghead rocks about said fore-and-aft pivot means during at least a portionof the upwardly swinging movement of the rearward portion of thesubframe to raise the cutter bar from its horizontal position to itsraised position.
 15. The invention defined in claim 14 wherein thesecond linkage means is connected to the rearward portion of thesubframe offset from the fore-and-aft centerline of the tractor and thesubframe arms are reversible so that the point of connection between thesubframe and the second linkage means is located in alternate positionswhen the arms are reversed.
 16. The invention defined in claim 14wherein the tractor includes a rearwardly extending drawbar and thefirst linkage means includes a chain interconnecting one of said arms tothe drawbar.
 17. The invention defined in claim 16 and including a chainoperative between the drawbar and the main frame to limit the downwardmovement of the main frame.
 18. A mower attachable to a tractor having avertically adjustable hitch and a rearwardly extending drawbar, saidmower comprising: a vertically adjustable main frame mounted on thetractor hitch; a pivot means on the main frame; a subframe swingablymounted on said pivot means; a first linkage mEans connecting thesubframe to the tractor to cause the subframe to pivot relative to themain frame as the main frame raises; a flexible linkage between thedrawbar and the main frame for limiting the downward movement of themain frame to establish the lowermost operating position of the mower; atransversely extending support structure having one end pivotallyconnected to the main frame and having a generally fore-and-aft pivotmeans adjacent to its outer end; a mower driving head pivotally mountedon said fore-and-aft pivot means; a cutter bar connected to andextending laterally outwardly from the driving head and operativelydriven thereby; and a second linkage means operatively connecting thedriving head to the subframe so that the driving head rocks about saidfore-and-aft pivot means at least during a portion of the rockingmovement of the subframe relative to the main frame to raise the outerend of the cutter bar during at least a portion of the raising of themain frame.
 19. The invention defined in claim 18 wherein said firstlinkage means and said flexible linkage means comprise a chain havingone end connected to the main frame, the other end connected to thesubframe, and connected to the drawbar intermediate its opposite ends.20. A mower comprising: a frame means; a transversely extending supportstructure having one end pivotally connected to the frame means andhaving a generally fore-and-aft pivot means adjacent to its outer end; amower driving head pivotally mounted on said fore-and-aft pivot means; acutter bar connected to and extending laterally outwardly from thedriving head and operatively driven thereby and swingable with thedriving head about said fore-and-aft pivot means from a generallyhorizontal operating position, to an upwardly and outwardly inclinedraised position, and thereafter to an upwardly and inwardly inclinedfolded transport position; a linkage means operatively connecting thedriving head to the frame means for rocking the driving head and thecutter bar from said operating position to said raised position as theframe means raises; and locking means operative to lock the linkagemeans to the support structure when the driving head and cutter bar arerotated to said transport position.
 21. The invention defined in claim20 wherein the linkage means includes an apertured element, and thelocking means includes a generally upright member, extending upwardlyfrom the supporting structure and extendible through the aperturedelement when the cutter bar is shifted to its transport position, andpin means extendible through the upright member above the aperturedelement to lock the apertured element on the upright member.
 22. A mowerattachable to a tractor having a vertically adjustable hitch and arearwardly extending power take-off shaft, said mower comprising: avertically adjustable main frame mounted on the tractor hitch andincluding a generally U-shaped member having generally upright legs; apair of transversely aligned pivots mounted on the opposite legs; asubframe swingably mounted on said pivots and including a pair of armsrespectively mounted on the respective pivots and a rearward portioninterconnecting the arms rearwardly of the pivot means; a first linkagemeans connecting one of said arms to the tractor forwardly of the pivotmeans to cause the rearward portion of the subframe to raise relative tothe main frame as the main frame raises; a transversely extendingsupport structure having one end pivotally connectible to the main frameat alternate locations on opposite sides of the tractor centerline andhaving a generally fore-and-aft pivot means adjacent its outer end; amower driving head pivotally mounted on said fore-and-aft pivot means; acutter bar connected to and extending laterally outwardly from thedriving head and operatively driven thereby; a drive system connectingthe power take-off shaft to the driving head and including a drivesheave rotatably supported on the main frame for lateral adJustmentbetween alternate positions on opposite sides of the centerline andconnected to the power take-off shaft by a drive shaft, a driven sheavedrivingly connected to the driving head coaxial with the fore-and-aftpivot means, and a belt drive interconnecting the drive and drivensheaves; and a second linkage means operatively connecting the drivinghead to the rearward portion of the subframe, at least a portion of thesubframe being reversible so that the second linkage means is connectedto the subframe at alternate locations corresponding to the alternatelocations of the support structure.
 23. The invention defined in claim22 and including a spring means connected to the driving head and therearward portion of the subframe substantially the same location as thesecond linkage means.
 24. A mower comprising: a vertically adjustablemain frame, a subframe swingably mounted on the main frame andoperatively connected to the main frame for vertical adjustmenttherewith and rocking movement relative thereto as the main frameraises; a transversely extending support structure having one endpivotally connected to the main frame and having a generallyfore-and-aft pivot means adjacent its outer end; a mower driving headpivotally mounted on said fore-and-aft pivot means; a cutter barconnected to and extending laterally outwardly from the driving head andoperatively driven thereby; a tension spring means operatively connectedto a portion of the subframe that raises at a more rapid rate than themain frame during the raising of the main frame; means connecting thespring means to the driving head at a point offset from the fore-and-aftpivot means so that the force exerted by the spring means tends torotate the driving head in the opposite direction from the weight of thecutter bar to partly counterbalance the weight supported at the outerend of the cutter bar, the spring means also exerting a force tending torotate the supporting structure upwardly about its pivot connection tothe main frame to partly counterbalance the weight supported on theinner end of the cutter bar; and linkage means operatively connectingthe driving head to the subframe so that the driving head is rockedabout said fore-and-aft pivot means to raise the outer end of the cutterbar at least during a portion of the rocking movement of the subframerelative to the main frame.
 25. The invention defined in claim 24wherein the means connecting the spring to the driving head includes achain connected in parallel with the spring means to limit the extensionof the spring means to a predetermined amount, the chain transmittingthe vertical movement of the subframe directly to the driving head aftersaid predetermined amount of spring extension to raise the driving headabout the pivot connection between the support structure and main frame.26. A mower attachable to a tractor having a vertically adjustable hitchand comprising: a vertically adjustable main frame mounted on thetractor hitch; a subframe swingably mounted on the main frame; a firstlinkage means connecting the subframe to the tractor to cause thesubframe to pivot relative to the main frame as the main frame raises sothat a portion of the subframe raises at a faster rate than the mainframe; a transversely extending support structure having one endpivotally connected to the main frame and having a generallyfore-and-aft pivot means adjacent its outer ends; a mower driving headpivotally mounted on said fore-and-aft pivot means; a cutter barconnected to and extending laterally outwardly from the driving head andoperatively driven thereby; a spring means operatively connected to oneof said frames and to the driving head for partly counterbalancing theweight of the driving head and the cutter bar; and a flexible elementoperatively connected to the driving head at a point offset from thefore-and-aft pivot means and to said portion of the subframe to causethe cutter bar to raise about said fore-and-aft pivot means during thElatter portion of the raising motion of the main frame, the flexibleelement being provided with a predetermined amount of slack when thecutter bar is in a generally horizontal operating position, which slackis taken up during the initial raising movement of the main frame andpermits a predetermined amount of downward movement of the outer end ofthe cutter bar so that the cutter bar follows the contour of the ground.27. The invention defined in claim 26 wherein the flexible element isconnected to the driving head through a lever swingably connected to thedriving head about a generally fore-and-aft axis and engageable with anabutment on the driving head to transmit the lifting force exerted bythe flexible element.
 28. The invention defined in claim 27 andincluding a pulley mounted on the subframe, the flexible element beingtrained around said pulley so that the vertical movement of the subframeportion results in a generally horizontal force, which is exerted on thedriving head through the flexible element, the lever, and the drivinghead abutment.